Gear-type hydraulic machine

ABSTRACT

A gear-type hydraulic machine, wherein fluid is conveyed between gear teeth of two mating gearwheels, includes an internal gear rotatably mounted in the machine and a smaller inner external gear mounted in the machine on journals and meshing with the internal gear. The pressure and the suction sides formed between the cooperating gear teeth are separated exclusively by the mating or meshing teeth. The numbers of teeth of the two gears differ sufficiently that a substantial part of the gear peripheries run out of engagement to define a crescent-shaped zone between the gears. This crescent-shaped zone communicates, through suitably dimensioned leakage passages or gaps, with the respective pressure and suction sides of the machine in order for intermediate pressure to build up in the crescent-shaped zone. This intermediate pressure operates to reduce substantially the radial thrust applied to the smaller inner gear by the pressure on the pressure side.

United States Patent [72] Inventors Hermann Harie Freiolshelm; SiegfriedEisenmann, Neclutrsulm, both of Germany [21] Appl. No. 876,370 [22]Filed Nov. 13, 1969 [45] Patented Nov. 9, 1971 [73] Assignee Furstlichl-lohenzollernsche Huttenverwattung Laucherthal Laucherthal,Hohenzollern, Germany [32] Priority Nov. 18, 1968 [33] Germany [3 1 P 1809 445.6

[54] GEAR-TYPE HYDRAULIC MACHINE 22 Claims, 5 Drawing Figs.

[52] U.S. C1 418/73, 417/310,4l8/81,4l8/133,4l8/171 [51] Int. Cl F01c1/10, FOlc 19/08 F01c 21/00 [50] Field of Search 418/73, 74, 81, 133,171;41 /31O [56] References Cited UNITED STATES PATENTS 2,124,140 7/1938Fosteret a1. 418/73 2,159,720 5/1939 Wahlmark 417/310 PrimaryExaminer-Carlton R. Croyle Assistant ExaminerWilbur .1. GoodlinAn0rneyMcGlew and Toren ABSTRACT: A gear-type hydraulic machine, whereinfluid is conveyed between gear teeth of two mating gearwheels, includesan internal gear rotatably mounted in the machine and a smaller innerexternal gear mounted in the machine on journals and meshing with theinternal gear. The pressure and the suction sides formed between thecooperating gear teeth are separated exclusively by the mating ormeshing teeth. The numbers of teeth of the two gears differ suffieientlythat a substantial part of the gear peripheries run out of engagement todefine a crescent-shaped zone between the gears. This crescent-shapedzone communicates, through suitably dimensioned leakage passages orgaps, with the respective pressure and suction sides of the machine inorder for intermediate pressure to build up in the crescent-shaped zone.This intermediate pressure operates to reduce substantiaily the radialthrust applied to the smaller inner gear by the pressure on the pressureside.

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HE'Rnnwu 'm'ime SIEGTRIEID EISENHIW R'ITORNE VS GEAR-TYPE HYDRAULICMACHINE BACKGROUND OF THE INVENTION Gear-type hydraulic machines,wherein a fluid is conveyed between the gear teeth of two mating gears,of which one is an internal gear rotatably mounted in the machine andthe other is a smaller inner external gear mounted in the machine onjournals, are well known in the art. They are low-pressure pumps, whichare built normally for pressure heads not exceeding l atmospheres gauge.In these pumps, the teeth of the internal gear are circular arcuateteeth, and the inner gear has one tooth less than the outer gear. Thepressure heads which can be generated by such pumps are not very highbecause, at a point diametrically opposite the point where the pitchcircles of the inner and outer gears meet, the suction and pressuresides of the machine are separated exclusively by the clearance betweenthe crest of one tooth of the inner gear and the crest of one tooth ofthe outer gear.

There are also known high-pressure pumps in which an internal gearmeshes with an inner external gear. In such highpressure pumps, thedifference between the numbers of teeth, or the design of the gearteeth, or both, is such that, at a point diametrically opposite thepoint where the pitch circles of the two gears make contact, there is agap between the internal gear and the inner external gear. This gap isfilled by a substantially crescent-shaped body, which has an internalarcuate surface in sliding contact with the crests of the teeth of theinner gear, and an external arcuate surface in sliding contact with thecrest of the teeth of the outer gear. In this type of pump, the fillingbody creates the seal between the suction and the pressure slides.

The efficiency of pumps of this type, which are high-pressure pumps,intended to generate pressure heads of 100 atmospheric gauge and more,remains satisfactory for as long as there is no wear. However, apartfrom wear being liable to occur, these pumps also have other drawbacks.

In the first place, the production cost of such machines is fairly highbecause the filling member must be machined very precisely. Nonnally,this member is intended to cooperate with the ground tooth crests of theinner and outer gears in the addendum cylinders of the gears. Increasingwear of the filling member causes a considerable reduction in thepumping efficiency of such pumps.

In order to overcome this difficulty, it has already been proposed tomount the external peripheral surface of the internal ring gear in acradlelike member surrounding the outlet port, with the filling memberinterposed movably between the inner and outer gears. However, this formof construction is likewise costly, and it has the further drawback ofthe direction of rotation of the pump not being reversible, as is nowfrequently required. Another major drawback of this form of constructionis that the inner gear must withstand the full delivery pressure on thepressure side, which tends to bend the shaft which carries the innergear and which is journaled in the body of the machine. This also hasthe effect of promoting wear. Finally the sealing surface between thepressure and suction sides on the outside of the internal ring gear isconfined to approximately the width of a single tooth crest. This isalso a defect of this form of construction.

SUMMARY OF THE INVENTION This invention relates to gear-type hydraulicmachines and, more particularly, to a gear-type hydraulic machinewherein the fluid is conveyed between the teeth of a rotatably mountedinternal ring gear in a smaller diameter inner external gear, with thepressure and suction sides between the cooperating gear teeth of the twogears separated exclusively by the mating teeth. Even more particularly,the invention is directed to a gear-type hydraulic machine of this kindwhich is economical to produce, which is free of the above-mentioneddisadvantages, which can be used as a high-pressure gear pump of simpledesign, and which is capable of being so constructed that pressurefluctuations of the fluid delivered by the pump are low for this kind ofpump.

In accordance with the invention, the gear-type hydraulic machine is sodesigned that the thrust of the high-pressure fluid, which applies aone-sided bending moment to the shaft of the inner gear, is compensatedby the generation of a counterthrust. Also, the machine is designed tobe suitable for highpressure operation, for operation with a wide rangeof speeds, or for both.

In further accordance with the invention, a gear-type hydraulic machineof the mentioned kind is so designed that the numbers of teeth of thetwo gears differ sufficiently that a substantial part of the peripheriesof the two gears when out of engagement with each other, defining acrescent-shaped zone, between the gears, in which the gear teeth are notin meshing engagement. This zone communicates, through suitably designedleakage gaps or passages, with the pressure and suction sides,respectively, to develop an intermediate pressure in the crescent-shapedzone, this intermediate pressure operating substantially to reduce theradial thrust effective on the inner gear due to the pressure existingon the pressure side.

In such pumps, the inlet and outlet ports for the fluid, which areprovided at least in one and preferably only in one of the sidewallsbetween which the gears revolve, should be as close to the point ofcontact of the pitch circles of the gears as the creation of asatisfactorily separating seal will permit. In the opposite directions,these ports should, in principle, extend far enough for a pumpingchamber, between two teeth on the inner gear and two teeth of the outergear, not to open after having passed across the entry port until thischamber has ceased to be in communication with the port. Conversely, thesame applies on the side of the outlet port.

In such a pump, relatively favorable conditions arise if the angulardistance, about the axis of the internal gear, of the far ends of theusually roughly arcuate suction and pressure ports, from the point wherethe pitch circles of the two gears make contact, is less than andpreferably between 40 and 60. The pressure existing in the region of theport through which the fluid leaves or enters at high pressure will thenexert a thrust on the inner gear directed away from the port and towardsthe axis of the inner gear. The circumstance that, in the inventionconstruction, the crescent-shaped zone is filled with fluid at anintermediate pressure operates to generate a further inward thrust whichacts on the inner gear. The line of action of this thrust is likewiseradial and extends through the center of the inner gear and the point ofcontact of the two pitch circles. By correctly dimensioning the leakageclearances this thrust, which is generated by a relatively low pressureacting within a relatively large angular region, can be made tocompensate exactly that component, of the first above-mentioned radialthrust generated on the pressure side, which is directed radiallyinwardly from the point of contact of the two pitch circles. The totalinward thrust acting on the inner wheel thus can be reduced by as muchas about 30 to 40 percent. Another advantage of the inventionconstruction is that the forces acting on the internal gear likewise canbe partly compensated. However, this effect on the internal gear is ofsecondary importance, because the internal gear can be supported aroundits entire periphery so that its specific hearing pressure is relativelylow.

Tests have disclosed that, despite the leakage which, in the inventionconstruction, is deliberately allowed in the regions of the ends of theports remote from the point of contact of the pitch circles, a verysatisfactory pumping efficiency nevertheless can be achieved because theloss due to this leakage is relatively small. This advantage overconventional pumps having circular arc tooth profiles on the internalgear is primarily due to the fact that the separating seal, betweenthose ends of the pressure and suction sides remote from the point ofpitch circle contact, is not limited to a single point but is dividedbetween two points, namely one at each end of the crescentshaped zone.This creates a kind of labyrinth effect.

Preferably the arrangement may be such that the inlet and outletregions, i.e. the angular regions occupied by the suction and pressureports, are separated in the peripheral direction by at least a halftooth division from the point of pitch circle contact, and that at leastone of these regions extends peripherally to a point that is slightlyless than one tooth division away from the point where the two gears runout of or into engagement. This form of construction ensures that afluid-filled chamber, between two neighboring teeth of the internal gearand two teeth of the inner gear, will open already into communicationwith the crescent-shaped zone while it still slightly overlaps the endof the relative inlet and/or outlet port. The leakage thus can bedetermined exactly by choosing the degree of this overlap. It isunnecessary that, in this region, there should be a certain amount ofclearance between cooperating tooth flanks. In fact it is permissible,and in practice this will usually be the case, for the meshing teetheven in this region to maintain close sliding contact, at least at oneof the ports.

The required leakage naturally can be created also by suitably designingthe gear teeth. However, this is more difficult to do. If the wall whichcontains the inlet and the outlet ports is arranged to be angularlyslightly adjustable, the intermediate pressure can be controlled byappropriate adjustment which permits the overlap on the loworhigh-pressure side to be increased and the other reduced, or the twooverlaps to be made equal on both sides.

It follows from what has been said that the pressure in thecrescent-shaped zone can be regulated according to the requirements ofthe design by increasing or reducing the leakage at the suction orpressure side until this pressure is of the desired magnitude.

Although the gear-type hydraulic machine according to the invention canbe operated to function as a hydraulic motor, it is primarily intendedto work as a gear pump. ln this case the pressure side is that at theoutlet port and the suction side is at the inlet port. The intermediatepressure zone then will extend between these two sides.

Preferably a gear-type machine according to the invention is arranged tobe reversible. This can be done by designing the chamber in which thetwo meshing gears revolve, including the inlet and outlet ports, so thatthe layout is symmetrical about a plane containing the axes of rotationof the two gears.

The choice of an appropriate gear tooth profile is of paramountimportance in a correctly designed machine according to the invention.lnvolute tooth flanks introduce certain difficulties. The inner gearmust have a reasonable diameter to provide a sufficiently longperipheral region for the accommodation of the inlet and outlet portsbetween the point of contact between the pitch circles and the pointswhere the two gears run out of or into engagement. In the case of arelatively large inner gear and a consequent small difference betweenthe numbers of teeth on the internal gear and the inner gear, involutetooth flanks would create interference in the regions where the twogears run out of and into engagement.

This difficulty can be overcome by tip relief of the involute gearflanks. A cycloidal tooth flank is even better. However, it is preferredto provide the internal gear with gear teeth having circular arc flankswhich meet at the tip. In such teeth, the tooth crests therefore arereduced to zero width. This form of construction provides not onlyfavorable sealing tooth flank engagement but also substantiallypressure-free sliding contact between the teeth of the gears for as longas they remain in mesh. It is of major importance that it should bepossible to grind such tooth flanks on the internal gear with arelatively simple gear grinding machine and in a gear-type hydraulicmachine comprising an internal gear the invention enables the toothflanks of such a gear to be produced with a heretofore unattained degreeof precision. This precision permits backlash to be diminished, wear tobe reduced and the contact pressure to be more accurately controlled.Undesirable clearances and leakage are also reduced.

That this novel type of gear tooth can be used is the result of theproposed design features of the machine since, in conventional pumps,the employment of similar teeth would create very considerable sealingdifficulties. ln a pump according to the invention the clearance curveat the roots of the teeth, that is to say the bottoms of the gapsbetween neighboring teeth, is slightly increased to ensure that thegrinding tool will clear the teeth at the roots when grinding theflanks.

Another major advantage of the proposed tooth profile is that the gapsbetween neighboring teeth are relatively large, in other words that thefluid-filled space available between two teeth on the internal gear andtwo teeth of the inner gear is relatively large. This, in turn, permitsa finer circular pitch to be used, and nonuniformity of flow of thedelivered fluid to be substantially diminished.

Another advantage of the proposed tooth profile is that during thedisplacement of the fluid trapped between the gear teeth as these comeinto mesh, there is no wide tooth crest abruptly penetrating into thefluid to displace a relatively large volume but only the sharp edge atthe tip enters the fluid. Finally, yet another advantage of the proposedtooth profile is that it permits a wider choice of the differencebetween the numbers of teeth on the internal and inner gears.

More particularly, the tooth flanks may meet at the tip at an anglebetween and 140. An angle between 100 and 1 10 is preferred. lt is alsopreferred that the relatively remote flanks of two neighboring teethshould form parts of the same circular cylinder surface.

The radius of the circle defining the curvatures of the internal gearteeth may with advantage be about 75 percent to 90 percent, preferablybetween 80 percent and percent, of the radius of the addendum circle ofthe internal gear.

Moreover, the height of the teeth of the internal gear may withadvantage be equal to about half the pitch of the internal gear teeth.

It is also preferred that the width of the gaps between the teeth at theroots of the teeth of the internal gear should be about 40 percent to 60percent of the thickness of the roots of the teeth.

The above-specified dimensions are by no means obligatory, but they haveproved to be essential to a satisfactory design of a pump according tothe invention.

The profile of the teeth of the inner gear is preferably generated byrolling the inner gear on the internal gear. Such an inner gear may withadvantage be produced by first providing a correctly shaped mold andthen sintering the gear. Alternatively, the inner gear may be producedwith the aid of a suitable gear-cutting machine of the nongeneratingshaping or of the generating type. Finally the inner gear also may beproduced by hobbing and honing on a machine using the generating rollprinciple.

With reference to the number of teeth, it should be mentioned that theinternal gear preferably may have only one or two teeth more than theinner gear. The lesser the number of teeth of the internal gear, thelesser will be the difference between the numbers of teeth. The moreteeth on the internal gear the greater will be the difference betweenthe numbers of teeth of the two gears.

In order to locate the gear axes precisely, and in order to prevent wearin the bearings, particularly during starting up and at low angularvelocities, in accordance with a further feature of the invention, thefluid forced through the clearances between the side faces of the gears,the side face of the casing and the side face of a thrust member iscollected in annular grooves in the casing, thrust member or both. Thecollected fluid is then conducted through bores in the casing or in thethrust member or in both, and partly also axially through bores in thegears, and supplied at limited pressure to hydrostatic bearing surfacesor to collecting pockets associated with hydrodynamic bearings, or toboth, the fluid being conducted to the hydrodynamic bearings alone ifonly hydrodynamic bearings are provided. This arrangement may beemployed also, with the same advantages, in other types of gear pumps orhydraulic motors. Conveniently, the thrust member has the form of aplate which is urged by fluid pressure against one face of each of thegears.

In order to asure maintenance of uniform clearances over the entire sidefaces and irrespective of the difference between the pressures of thefluid escaping from the working chambers, ports and intermediate zone,areas defined by O-rings for biasing the thrust member against the sidesof the gears, are pressurized through axial ducts traversing the thrustmember and communicating with the working chambers, the ports, or thecrescent-shaped intermediate zone, respectively, with which these areasare axially aligned.

An object of the invention is to provide an improved geartype hydraulicmachine wherein a fluid is conveyed between teeth of two mating gearsincluding an internal ring gear and a smaller diameter external gear andwherein the pressure and suction sides between the meshing gear teethare separated exclusively by the meshing teeth.

Another object of the invention is to provide such a machine which iseconomical to produce and which can be used as a high-pressure gear pumpof simple design.

A further object of the invention is to provide such a machine in whichpressure fluctuations of the fluid delivered by the pump are low.

Another object of the invention is to provide such a machine in whichthe thrust of the high-pressure fluid, applying a bending moment to theshaft of the inner gear, is compensated by the generation of a counterthrust.

A further object of the invention is to provide such a machine which issuitable for high-pressure operation, for operation within a wide rangeof angular velocities, or both.

Another object of the invention is to provide such a machine in whichthe teeth of the internal ring gear have a novel profile.

For an understanding of the principles of the invention, reference ismade to the following description of typical embodiments thereof asillustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS In the Drawings: X

FIG. 1 is a pump according to the invention shown in a section taken onthe line A-A in FIG. 2;

FIG. 2 is a pump according to the invention shown in a sec tion taken onthe line DD in FIG. 1;

FIG. 3 is a pump according to the invention shown in a section taken onthe line 8-8 in FIG. 2;

FIG. 4 is a fragmentary section taken on the line CC in FIG. 2; and

FIG. 5 is a pump according to the invention showing a preferred geartooth profile.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The theoretical considerationsupon which the design of a pump embodying the invention is based willfirst of all be described with reference to FIG. 5. In this drawing aninternal ring gear 51 which revolves about a center at 50 meshes withthe external teeth of a smaller diameter inner external gear 53 whichrevolves about a center at 52. The illustrated internal ring gear haseleven internal teeth 54, whereas the inner gear 53 has nine externalteeth 55. The inlet and outlet ports 56 and 57, in the illustratedembodiment, are located, symmetrically with reference to a symmetryplane containing the two centers 52 and 50, in one sidewall of a chambercontaining the two gears.

It will be understood from FIG. 5 that the flanks of the teeth 54 of theinternal gear 51 form parts of cylinder surfaces having the same radiusr. Moreover, the teeth are so disposed and designed that the relativelyremote flanks of each pair of adjacent teeth form parts of the samecylinder surface. In the sectional drawing, these flanks appear as arcsof a common circle. Moreover, the height h of the teeth, the thickness 8of the roots of the teeth and the width b of the clearance gaps betweenthe roots of adjacent teeth of the internal gear are marked in thedrawing. The pitch 1 of the teeth is likewise shown. The pitch of theteeth is understood to be the distance between similar points onadjacent teeth, for instance, in the present case, between the crests ofthe teeth if these were assumed to be a gearwheel of infinite diameter.In practice, in an internal gear, this distance can be measured on thepitch circle, as indicated in FIG. 5.

The compensation, according to the invention, of the radial pressuregenerated on the pressure side will now be explained. Let it be assumedthat the two gearwheels work in a pump and revolve in the direction ofthe arrow in FIG. 5. The port 56 then will be the suction port and theport 57 the pressure port through which the pump delivers the fluid. Thefull pressure head of the pump then will be generated around an angularregion of the inner gear which corresponds roughly to the angular extentof the port 57. The resultant thrust R then will act at the center ofthe inner gear. Since, in the lower part of FIG. 5, there will begenerated a medium pressure which is intermediate the suction pressureand the delivery pressure, this intermediate pressure generates a thrustM at the center of the inner gear. By correctly dimensioning theavailable leakage cross sections between the teeth at the transitionbetween the suction side and the intermediate pressure zone, it ispossible to ensure that the magnitude of that force M will be exactlyequal to the magnitude of that component of force R acting in thesymmetry plane in FIG. 5. When this is the case, the only remainingradial thrust on the bearings of the inner gear 53 will be that markedL. This is only about of the total magnitude of R. The proposed pressurecompensation not only relieves the load on the bearings of the innergear 53 but also that on the internal ring gear 51. A force equal inmagnitude to R but in the opposite direction, as well as a force equalto M but opposed thereto in direction, act simultaneously on theinternal gear, so that there is also a partial compensation of these twoforces.

In the embodiment of the invention shown in FIGS. 1 through 4, aninternal ring gear 2 is rotatably mounted within casing l, with theexternal peripheral surface of ring gear 2 providing radial locationthereof. An inner gear 3, having external teeth, is rotatably mounted incasing l and is axially located therein by means of its side faces. Gear3 is radially located by a stub axle l7 journaled in a bearing in casingI and the stub axle 9 journaled in a bearing in a thrust member 12. Theexternal peripheral surface of the thrust member 12 preferably has thesame overall diameter as the outer diameter of internal ring gear 2.Thrust member 12 is axially displaceable within casing l, but cannotrotate therein. The axial movement of thrust member 12 is limited by acover 13 facing the outer surface of thrust member 12 and threadedlysecured to casing 1 to form a tight seal with the latter.

A torsionally elastic drive shaft 16 is secured to rotate with innergear 3, being connected to the latter by a gear coupling 19 and stubshaft 17. Shaft 16 is rotatably supported in cover 13, as byantifriction bearings 14, for example, which are externally sealed bysealing means 15 surrounding shaft 16.

The involute gear teeth, which are shown in FIGS. 1 through 4 as analternative to the previously described preferred type of gear teeth,are provided with slight tip relief in such a way that, within theentire region of tooth engagement between the points of intersection 4,4', of the addendum circles, the clearance between the tooth flanks isonly 0.02 to 0.05 mm. The points of intersection of the addendum circlesand the point of contact of the pitch circles, or briefly the point offull engagement, thus sharply separate the suction side, the pressureside and the intermediate pressure zone of the machine. The ports 5 and5 through which the pumped fluid enters or leaves, in accordance withthe direction of rotation, are located in the sidewall of casing 1.However, it is naturally also possible, in a manner known in the art, toadmit or discharge the pump fluid peripherally into and from internalring gear 2, through openings in the periphery of this gear into thespace between the teeth or correspondingly to admit or discharge thepumped fluid from the inside in a similar way between the external gearteeth of inner gear 3. This may have advantages under certain workingand design conditions, for

instance when the gears are cylinder gears of considerable axial length,for handling large volumes, or if the gear diameters are small.

In the embodiment of the invention illustrated in FIGS. 1 through 8, theexternal periphery of internal ring gear 2 is mounted in a bearingrecess in casing l, and the stub shafts of inner external gear 3 aremounted in bearing recesses in casing l and thrust bearing l2,respectively. The bearing recesses form two hydrodynamic bearingsurfaces 26 separated by an interposed hydrostatic bearing surface 29communicating with ducts 27 through bores 28. Fluid that has been forcedthrough the clearances between the side faces of the gears and the sidefaces of casing I and thrust member 12, respectively, and which has beencollected in annular grooves 32 and 35 in casing l, enters ducts 27through bores 33 which communicate with grooves 32 and 35. This fluidalso enters partly through axial bores 7 and 8 in the gears, and is thusconducted at limited pressure to hydrostatic bearing surfaces 29, 36, orinto pockets 43 (FIG. 4), when only hydrodynamic bearings are used.

This limited pressure may be controlled by a pressure regulating valve42 in casing l, valve 42 comprising a plunger 39 which, when necessary,uncovers an outlet opening 40 against the bias of a spring 41. Thislimited pressure also may be admitted into areas 22 on the outer surfaceof thrust member 12, for generating axial thrust on thrust member 12,the areas 22 being defined and tightly sealed by the O-rings 241.However, in a preferred form of construction the pressure-generatingareas are pressurized through axial bores 23 traversing thrust member12, to transmit the pressures existing in working chambers or ports and5, or the intermediate zone that are in axial alignment with thecorresponding thrust-generating areas.

Considerable pressure fluctuations during operation, in thecrescent-shaped intermediate zone, also may be damped and equalized by apressure-equalizing device 34 (FIGS. 2 and 4), including a piston 38exposed to the pressure in the crescentshaped zone and displaceableagainst the bias of a spring 37. At the same time, this arrangement alsosuppresses pressure fluctuations in the leakage gaps. The pumped fluid,which is expelled from the hydrodynamic bearings, is collected inannular grooves 25 and delivered through bores 20, 21 and 11 to a tankor the like.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:

1. In a gear-type hydraulic machine, wherein fluid is conveyed betweengear teeth of two mating gearwheels, one of which is an internal gearrotatably mounted in the machine and the other of which is a smallerdiameter inner external gear mounted in the machine on journals, andwherein the pressure side and the suction side, formed between theintermeshing teeth of the two gears, are separated solely by the matingteeth: the improvement comprising the numbers of teeth of said two gearsdiffering sufficiently for a substantial part of the gear peripheries torun out of engagement with each other to define a crescent-shaped zonebetween said gears and in which the gear teeth are not in engagement;and suitably dimensioned leakage paths connecting said crescentshapedzone with the pressure side and with the suction side to build up, insaid crescent-shaped zone, an intermediate pressure operatingsubstantially to reduce the radial thrust applied to said smallerdiameter inner gear by the pressure on the pressure side.

2. In a gear-type hydraulic machine, the improvement claimed in claim I,in which the fluid inlet and fluid outlet regions are separatedperipherally, by at least a half tooth division, from the point wherethe pitch circles of said two gears make contact; at least one of saidfluid inlet and fluid outlet regions extending peripherally, in adirection away from said point, to a point that is spaced slightly lessthan one tooth division from the adjacent peripheral end of saidcrescent-shaped zone.

3. In a gear-type hydraulic machine, the improvement claimed in claim 1,wherein said machine is a gear pump.

4. In a gear-type hydraulic machine, the improvement claimed in claim 1,wherein said machine is reversible.

5. In a gear-type hydraulic machine, the improvement claimed in claim 4,in which said machine has inlet and outlet ports; the space in whichsaid gears revolve, including said inlet and outlet ports, having asymmetrical configuration with reference to a symmetry plane includingthe axes of rotation of said gears.

6. In a gear-type hydraulic machine, the improvement claimed in claim t,in which said internal gear has gear teeth with circular arc toothflanks meeting at a common tip.

7. In a gear-type hydraulic machine, the improvement claimed in claim 6,in which said tooth flanks meet at said tip at an angle of to 140.

8. In a gear-type hydraulic machine, the improvement claimed in claim 7,in which said tooth flanks meet at said tip at an angle of 100 to 1 10.

9. In a gear-type hydraulic machine, the improvement claimed in claim 6,in which the radius of the circular arc of said tooth flanks of saidinternal gear is about from 75 percent to 90 percent of the radium ofthe addendum circle of said internal gear.

10. In a gear-type hydraulic machine, the improvement claimed in claim9, in which the radium of the circular arc of said tooth flanks of saidinternal gear is about from 80 percent to percent of the radium of theaddendum circle of said in ternal gear.

11. In a gear-type hydraulic machine, the improvement claimed in claim6, in which the height of said teeth of said internal gear isapproximately equal to half the pitch of said teeth of said internalgear.

12. In a gear-type hydraulic machine, the improvement claimed in claim6, in which the width of the gaps between the teeth at the roots of saidteeth of said internal gear is equal to about from 40 percent to 60percent of the thickness of said teeth at the roots thereof.

13. In a gear-type hydraulic machine, the improvement claimed in claim6, in which the shape of the external teeth of said inner gear isgenerated by rolling on said internal gear.

14. In a gear-type hydraulic machine, the improvement claimed in claim6, in which the number of teeth of said internal gear is one more thanthe number of teeth of said inner gear.

15. In a gear-type hydraulic machine, the improvement claimed in claim6, in which the number of teeth of said internal gear is two more thanthe number of teeth of said inner gear.

16. In a gear-type hydraulic machine, the improvement claimed in claim6, in which the relatively remote tooth flanks of adjacent gear teeth ofsaid internal gear from parts of a common cylinder surface.

17. In a gear-type hydraulic machine, the improvement claimed in claim1, including a casing in which said gears are rotatably mounted, saidcasing having a sidewall member engaging corresponding first sides ofsaid gears; a thrust member mounted in said casing and engagingcorresponding second sides of said gears; at least one of said membersbeing formed with annular grooves communicating with the clearances atthe side faces of said gears, to collect fluid forced into saidclearances; said casing and said thrust member having bearing recessesdefining, with said gears, hydraulic bearing recesses; ductscommunicating with said hydraulic recesses; and bores connecting saidannular grooves to said ducts to supply the collected fluid to saidhydraulic bearing recesses at a limited pressure.

13. In a gear-type hydraulic machine, the improvement claimed in claim17, in which said bores include bores extending radially of said wallmember of said casing.

with working chambers, inlet and outlet ports, or said crescent-shapedzone of said machine then axially aligned with said pressurized areas.

21. In a gear-type hydraulic machine, the improvement claimed in claim17, including a pressure relief valve communicating with said bores.

22. In a gear-type hydraulic machine, the improvement claimed in claim20, including a pressureequalizing device communicating with saidcrescent-shaped zone.

# IF i i Q

1. In a gear-type hydraulic machine, wherein fluid is conveyed betweengear teeth of two mating gearwheels, one of which is an internal gearrotatably mounted in the machine and the other of which is a smallerdiameter inner external gear mounted in the machine on journals, andwherein the pressure side and the suction side, formed between theintermeshing teeth of the two gears, are separated solely by the matingteeth: the improvement comprising the numbers of teeth of said two gearsdiffering sufficiently for a substantial part of the gear peripheries torun out of engagement with each other to define a crescent-shaped zonebetween said gears and in which the gear teeth are not in engagement;and suitably dimensioned leakage paths connecting said crescent-shapedzone with the pressure side and with the suction side to build up, insaid crescent-shaped zone, an intermediate pressure operatingsubstantially to reduce the radial thrust applied to said smallerdiameter inner gear by the pressure on the pressure side.
 2. In agear-type hydraulic machine, the improvement claimed in claim 1, inwhich the fluid inlet and fluid outlet regions are separatedperipherally, by at least a half tooth division, from the point wherethe pitch circles of said two gears make contact; at least one of saidfluid inlet and fluid outlet regions extending peripherally, in adirection away from said point, to a point that is spaced slightly lessthan one tooth division from the adjacent peripheral end of saidcrescent-shaped zone.
 3. In a gear-type hydraulic machine, theimprovement claimed in claim 1, wherein said machine is a gear pump. 4.In a gear-type hydraulic machine, the improvement claimed in claim 1,wherein said machine is reversible.
 5. In a gear-type hydraulic machine,the improvement claimed in claim 4, in which said machine has inLet andoutlet ports; the space in which said gears revolve, including saidinlet and outlet ports, having a symmetrical configuration withreference to a symmetry plane including the axes of rotation of saidgears.
 6. In a gear-type hydraulic machine, the improvement claimed inclaim 1, in which said internal gear has gear teeth with circular arctooth flanks meeting at a common tip.
 7. In a gear-type hydraulicmachine, the improvement claimed in claim 6, in which said tooth flanksmeet at said tip at an angle of 80* to 140*.
 8. In a gear-type hydraulicmachine, the improvement claimed in claim 7, in which said tooth flanksmeet at said tip at an angle of 100* to 110*.
 9. In a gear-typehydraulic machine, the improvement claimed in claim 6, in which theradius of the circular arc of said tooth flanks of said internal gear isabout from 75 percent to 90 percent of the radium of the addendum circleof said internal gear.
 10. In a gear-type hydraulic machine, theimprovement claimed in claim 9, in which the radium of the circular arcof said tooth flanks of said internal gear is about from 80 percent to85 percent of the radium of the addendum circle of said internal gear.11. In a gear-type hydraulic machine, the improvement claimed in claim6, in which the height of said teeth of said internal gear isapproximately equal to half the pitch of said teeth of said internalgear.
 12. In a gear-type hydraulic machine, the improvement claimed inclaim 6, in which the width of the gaps between the teeth at the rootsof said teeth of said internal gear is equal to about from 40 percent to60 percent of the thickness of said teeth at the roots thereof.
 13. In agear-type hydraulic machine, the improvement claimed in claim 6, inwhich the shape of the external teeth of said inner gear is generated byrolling on said internal gear.
 14. In a gear-type hydraulic machine, theimprovement claimed in claim 6, in which the number of teeth of saidinternal gear is one more than the number of teeth of said inner gear.15. In a gear-type hydraulic machine, the improvement claimed in claim6, in which the number of teeth of said internal gear is two more thanthe number of teeth of said inner gear.
 16. In a gear-type hydraulicmachine, the improvement claimed in claim 6, in which the relativelyremote tooth flanks of adjacent gear teeth of said internal gear fromparts of a common cylinder surface.
 17. In a gear-type hydraulicmachine, the improvement claimed in claim 1, including a casing in whichsaid gears are rotatably mounted, said casing having a sidewall memberengaging corresponding first sides of said gears; a thrust membermounted in said casing and engaging corresponding second sides of saidgears; at least one of said members being formed with annular groovescommunicating with the clearances at the side faces of said gears, tocollect fluid forced into said clearances; said casing and said thrustmember having bearing recesses defining, with said gears, hydraulicbearing recesses; ducts communicating with said hydraulic recesses; andbores connecting said annular grooves to said ducts to supply thecollected fluid to said hydraulic bearing recesses at a limitedpressure.
 18. In a gear-type hydraulic machine, the improvement claimedin claim 17, in which said bores include bores extending radially ofsaid wall member of said casing.
 19. In a gear-type hydraulic machine,the improvement claimed in claim 17, in which said bores include boresextending axially of said internal gear.
 20. In a gear-type hydraulicmachine, the improvement claimed in claim 17, including a cover platesecured to said casing and engaging with the outer side of said thrustmember; said outer side of said thrust member being formed withpressurized areas defined by O-rings, for urging said thrust memberagainst the second sides of said gears; and axial ducts formed in saidthrust member and connecting said pressurized areas with workingchambers, inlet and outlet ports, or said crescent-shaped zone of saidmachine then axially aligned with said pressurized areas.
 21. In agear-type hydraulic machine, the improvement claimed in claim 17,including a pressure relief valve communicating with said bores.
 22. Ina gear-type hydraulic machine, the improvement claimed in claim 20,including a pressure-equalizing device communicating with saidcrescent-shaped zone.